Enhancing product streams from ethanol production

ABSTRACT

Processes are described herein for realizing an enhanced yield of ethanol and co-products from the by-products (e.g., stillage) of existing ethanol production processes, particularly processes for producing ethanol from biomass containing lignocellulosic material. Also described herein are product outputs of these processes having new and useful properties and systems implementing the processes.

CROSS-REFERENCE TO RELATED APPLICATIONS TECHNICAL FIELD

This application claims the benefit of U.S. Provisional PatentApplication No. 62/989,423 filed Mar. 13, 2020 and entitled “ENHANCINGPRODUCT STREAMS FROM ETHANOL PRODUCTION,” the entire contents of whichare hereby incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to energy production frombiomass sources. More specifically, the present disclosure relates toenhancing product and co-product yield from ethanol productionprocesses.

BACKGROUND

The production of ethanol from biomass involves a number of unitprocesses, each having various inputs and losses. Whole stillage as aby-product of distillation represents a considerable process loss,particularly for ethanol production from feedstocks containingsignificant amounts of starch and lignocellulosic material. Wholestillage can contain unrecovered ethanol and unfermentablecarbohydrates, the latter of which represent an unrealized potentialyield of ethanol. The fiber content of stillage solids can also makedesirable co-products of ethanol production (e.g., distillers corn oil(DCO) from corn-based ethanol production) less accessible for recovery.There is considerable interest in seizing the opportunities presented byethanol production by-products for additional product and co-productyield. However, challenges remain in that utilization of this materialto this end requires more intensive mechanical and chemical treatment,and therefore increased inputs of material resources and energy.

BRIEF DESCRIPTION OF THE FIGURES

The embodiments disclosed herein will become more fully apparent fromthe following description and appended claims, taken in conjunction withthe accompanying drawings. These drawings depict only typicalembodiments, which will be described with additional specificity anddetail through use of the accompanying drawings in which:

FIG. 1 illustrates an ethanol production plant 100 representative ofcurrent approaches used in the art.

FIG. 2 illustrates a part of a primary ethanol production plant modifiedaccording to an embodiment.

FIG. 3 illustrates a method for producing a sugar from lignocellulosicmaterial in wet cake, in accordance with an embodiment.

FIG. 4 illustrates a process for pretreatment of wet cake in accordancewith the embodiment of FIG. 3.

FIG. 5 illustrates a method for hydrolyzing lignocellulosic material inwet cake, in accordance with one embodiment.

FIG. 6 illustrates a process for enzymatic hydrolysis in accordance withthe embodiment of FIG. 5.

FIG. 7 illustrates an exemplary process for recovering cellulosicethanol in accordance with an embodiment.

FIG. 8 illustrates an exemplary process for recovering cellulosicethanol modified in accordance with the embodiment shown in FIG. 2.

FIG. 9 illustrates a process for co-product production from fermentedwet cake in accordance with an embodiment.

FIG. 10 illustrates an enhanced ethanol production plant and associatedmethods in accordance with particular embodiments.

FIG. 11 illustrates an enhanced ethanol production plant and associatedmethods in accordance with particular embodiments.

DETAILED DESCRIPTION

Reaping the potential benefits of utilizing ethanol productionby-products can depend to a significant extent on the ability to recoveradditional ethanol and co-products from them in a cost- andresource-effective manner. In one aspect, this can involve accomplishingextra treatment steps in a more efficient manner, so that good resultsare achieved with a judicious use of resources. Another aspect caninclude increasing the useful qualities of such products andco-products. In another aspect, resource-effectiveness can be enhancedby coupling these additional recovery processes with existing productionprocesses so as to take advantage of reusable inputs and by-products.

Processes are described herein for realizing an enhanced yield ofethanol and quality of co-products from the by-products (e.g., stillage)of existing ethanol production processes, particularly processes forproducing ethanol from starch-based biomass such as corn, or otherbiomass comprising lignocellulosic material. Also described herein areproduct outputs of these processes having new and useful properties.

Reference throughout this specification to “an embodiment,” “theembodiment,” “particular embodiments,” or “certain embodiments” meansthat a particular feature, structure, or characteristic described inconnection with that embodiment is included in at least one embodiment.Thus, the quoted phrases, or variations thereof, as recited throughoutthis specification are not necessarily all referring to the sameembodiment.

The phrase “operably connected to” refers to any form of interactionbetween two or more entities, including mechanical, electrical,magnetic, electromagnetic, fluid, and thermal interaction. Two entitiesmay interact with each other even though they are not in direct contactwith each other. For example, two entities may interact with each otherthrough an intermediate entity.

As shown in FIG. 1 presenting corn-based ethanol production by way ofexample, an ethanol production plant 100 can comprise a plurality ofunit operations and processes as follows. A corn feedstock is ground bya mill 102 to reduce the corn to particles of a selected size. In aparticular embodiment, the mill 102 can employ a dry-milling process,i.e., employing mechanical means of breaking or crushing the cornkernels into smaller pieces without the addition of any liquid.Dry-milling techniques include, by way of non-limiting example, hammermilling, roller milling, and ball-milling. The fractionated cornundergoes further processes designed to make available fermentablesugars from the carbohydrates (primarily starch) in the corn. Theseprocesses can include slurrying performed in a slurrying tank 104,cooking in a cook tank 106, and liquefaction in a liquefaction tank 108.The resulting mash is transferred to a fermentation tank 110, wheresimple sugars produced by these processes undergo fermentation toproduce ethanol. The resulting mixture of corn solids, water andethanol, termed beer, is then sent to a distillation system 112, whichstrips the ethanol from the beer, yielding an ethanol solution productstream and whole stillage—mostly non-fermentable solids and water—as aby-product. Residual water is removed from the ethanol solution in oneor more steps in a dehydration system 114.

The whole stillage can be further treated to recover co-products.Typically, this involves using separation equipment such as a centrifuge116 to separate the whole stillage into its solid and liquid fractions,respectively termed hereinafter as “wet cake” and “first thin stillage”or “centrate.” The wet cake can be combined with syrup produced byevaporating the thin stillage, and then dried to produce drieddistillers grains with solubles (DDGS), commonly utilized in animalfeed. Distillers corn oil can be extracted from the syrup produced byevaporating water from the first thin stillage, for example by usingevaporator 118.

The whole stillage by-product of typical ethanol production processes,referred to herein as “first whole stillage”, can contain significantamounts of polysaccharides that exited those processes in a stillunfermented or unfermentable state. For example, a considerable fractionof the lignocellulosic material (cellulose, hemicellulose, and lignin)and residual starch found in corn—much of it from corn fiber—may befound in first whole stillage from corn-based ethanol production. Firstwhole stillage, or more particularly the solid fraction thereof, cantherefore be used as a feedstock for processes designed to convert thesematerials into sugars that can be fermented to produce an additionalethanol stream, i.e., cellulosic ethanol. The extent to which this isaccomplished determines not only the additional ethanol yield from theinitial feedstock, but also the characteristics of the stillageby-product of this second-generation process, which in turn influencesthe quality and characteristics of co-products. Other processes exist bywhich fermentable solids may be separated or concentrated from theby-products of primary ethanol production. It is contemplated that anysuch material, which can be generally termed “fermentation residualmaterial”, can be used as a feedstock for processes described herein.Therefore while the term “wet cake” is used herein by way ofnon-limiting example to refer to such feedstock, the discussion isintended to apply generally to fermentation residual materials.

According to the present disclosure, a method comprising a two-stageacid pretreatment process can operate on a feedstock of wet cake fromprimary ethanol production to effectively break up a fraction of thelignocellulosic material contained therein and convert the starch,cellulose and hemicellulose in that fraction into oligomeric andmonomeric sugars.

In an embodiment, the composition of wet cake entering the process ismodified by treating the first whole stillage stream. More specifically,protein contained in the first whole stillage is removed therefrom so asto lower the protein content of the wet cake before further processing.In accordance with the embodiment, the first whole stillage is directedto equipment configured to remove a portion of the protein contained inthe first whole stillage. FIG. 2 shows part of the primary ethanolproduction plant illustrated in FIG. 1 modified in accordance with aparticular embodiment, in which the first whole stillage from thedistillation system 112 is passed—optionally with wash water—through ascreener 202 configured to filter the first whole stillage so that afiltrate stream containing a portion of the protein is separated fromthe first whole stillage before the filtered first whole stillage entersthe centrifuge 116. Equipment suitable for this purpose are known tothose of skill in the art with the aid of the present disclosure. Theseinclude pressure screen devices, paddle screen devices and centrifugeswith screens to allow protein to be separated which employ pressure,paddles or centrifugal force, respectively to bring a material to befiltered into contact with one or more screens by which liquid andconstituents dissolved or suspended therein are separated from solids.Washing may be used to aid in the separation of protein from the wholestillage. In a specific embodiment, the screener 202 includes one ormore screens each having a mesh size selected so as to separate liquidfrom the first whole stillage and thereby separate some of the proteinfrom the solids. In a more specific embodiment, the screener includes ascreen having a mesh size of from 100 openings/in² to 500 openings/in²,or more specifically any one of 100, 150, 200, 250, 300, 350, 400, 450,or 500 openings/in². In a particular embodiment, the screener includes aplurality of stages through which the first whole stillage passessequentially, where the plurality of stages may comprise screens ofdifferent mesh sizes.

After exiting the screener, the filtered first whole stillage is thenseparated by the centrifuge 116 into first thin stillage and wet cake,and the wet cake is subjected to processes such as the two-stage acidpretreatment process described below. In an aspect of these embodiments,the protein in the filtrate bypasses the two-stage acid pretreatmentprocess and can be recovered in a downstream stage.

In an embodiment as illustrated in FIG. 3, a method for producing sugarfrom lignocellulosic material in wet cake 300 can comprise a step ofwashing 302 the wet cake to remove a liquid fraction from the wet cake.The washing step can be accomplished in the screening step describedabove or employed in addition to or in alternative to the screeningdescribed above. In an acidification 304 step, an amount of an acid ismixed into the wet cake. Two stages of pretreatment are included in theembodiment, where a first pretreatment stage 306, comprises agitatingthe wet cake and the acid for a first pretreatment time at a firstpretreatment temperature. A second pretreatment stage 308 comprisespretreating the wet cake with the acid in a pretreatment reactor for asecond pretreatment time at a second pretreatment temperature.

This embodiment is illustrated further by way of example in FIG. 4.According to the embodiment, the method can comprise mixing an amount ofan acid into the wet cake. The acid is added in an amount so that theconcentration of the acid in the wet cake is from about 0.5 wt % toabout 7 wt %. The acid may be added in an amount so as to achieve a pHof the wet cake of from about 1.5 to about 2.5. The acid can be added tothe wet cake and mixed therewith using mechanical systems to achievethorough mixing. In one embodiment, as illustrated in FIG. 4, a mixer402 designed for mixing high viscosity fluids, also known as a pug millmixer or mingler, can be used for this purpose. By way of non-limitingexample, the acid used can be a mineral acid such as sulfuric,phosphoric, hydrochloric, hydrofluoric, formic, or nitric acid, or amixture thereof, or an organic acid such as maleic, oxalic, acetic, orfumaric acid, or a mixture thereof. As would be apparent to those havingskill in the art with the aid of the present disclosure, other acids maybe used to decrease the pH of the wet cake in accordance with presentembodiment.

In accordance with the embodiment, the first pretreatment stage cancomprise heating and agitating the acidified wet cake to beginhydrolysis of the lignocellulosic material in the wet cake. Heating maynot be necessary if the wet cake is already at a sufficiently hightemperature. In a particular embodiment, the acidified wet cake can betransferred to a pretreatment vessel 304 for this purpose. In a moreparticular embodiment, this vessel is a cone-bottomed tank equipped withan agitator, where agitation of the material is performed for a firstpretreatment time. In other embodiments, a horizontal or vertical pipecould be used for this step. In a particular embodiment, the acidifiedwet cake is heated before it is transferred to the pretreatment vessel404, for example while it is in the mixer 402. In another embodiment,the acidified wet cake is heated in the pretreatment vessel 404.

In a particular aspect of the two-stage acid pretreatment process, thisfirst pretreatment stage is accomplished without employing highpressures. In a particular embodiment, the first stage is conducted withthe acidified wet cake at a first pretreatment pressure that is fromslightly negative (about −1 psig) to about 10 psig. According to morespecific embodiments, the first pretreatment pressure can be from about−1 psig to about 5 psig, or from 0 psig to about 6 psig, or from 0 psigto about 10 psig.

The wet cake is heated to a first pretreatment temperature for the firststage of pretreatment. This can be done during acidification in themixer 402 or during agitation in the pretreatment vessel 404.Alternatively, the wet cake may be hot (e.g., 170° F. or above) as itexits from the first whole stillage decanter and therefore may not needto be heated further. In a particular embodiment, the first pretreatmenttemperature is from about 170° F. to about 225° F. According to morespecific embodiments, the first pretreatment temperature is from about180° F. to about 215° F., or from about 190° F. to about 200° F., orfrom about 170° F. to about 200° F., or from about 180° F. to about 225°F. In a particular embodiment, the first pretreatment pressure is atatmospheric pressure and the boiling temperature of pure water at theelevation at which this step is conducted is the upper limit for thefirst pretreatment temperature.

The first pretreatment time can be selected so as to achieve thoroughmixing of the acid and wet cake based on the mass of wet cake residentin this step. In a particular embodiment, the first pretreatment timecan be from about 10 minutes to about 300 minutes. In more specificembodiments, the first pretreatment time can be from about 30 minutes toabout 180 minutes, or about 20 minutes to about 120 minutes, or fromabout 5 minutes to about 90 minutes, or from about 15 minutes to about60 minutes.

The inventors have surprisingly found that, despite employing relativelylow pressure and temperature, the first pretreatment stage achieveseffective hydrolysis of cellulose and hemicellulose to a desired yieldof soluble sugars (e.g., glucose, xylose, galactose, arabinose, andmannose). In an embodiment, the first pretreatment stage provides apercent yield of soluble glucose of from about 10% to about 60%, or anaverage percent yield of from about 30% to about 45%. In a moreparticular embodiment, the percent yield of monomeric glucose from thefirst stage is from about 0% to about 10%, or an average percent yieldof from about 1% to about 4%. In another embodiment, the firstpretreatment stage provides a percent yield of soluble xylose of fromabout 80% to about 100%, or an average percent yield of from about 93%to about 97%. In a more particular embodiment, the yield of monomericxylose from the first stage is from about 0% to about 25%, or an averagepercent yield of from about 5% to about 10%. In another embodiment, thefirst pretreatment stage provides a percent yield of soluble arabinoseof from about 85% to about 100%, or an average percent yield of about95% to about 99%. In a more particular embodiment, the yield ofmonomeric arabinose from the first stage is from about 0% to about 95%,or an average percent yield of about 45% to about 60%. In still anotherembodiment, the first pretreatment stage provides a percent yield ofsoluble galactose of from about 55% to about 100%, or an average percentyield of about 90% to about 95%. In a more particular embodiment, theyield of monomeric galactose from the first stage is from about 0% toabout 50%, or an average percent yield of about 10% to about 20%. Instill another embodiment, the first pretreatment stage provides apercent yield of soluble mannose of from about 30% to about 100%, or anaverage percent yield of about 75% to about 90%. In a more particularembodiment, the yield of monomeric mannose from the first stage is fromabout 0% to about 75%, or an average percent yield of about 10% to about25%.

In another aspect of the two-stage acid pretreatment process, inaddition to effective conversion of lignocellulosic material to sugars,the production of unfermentable compounds that can arise from thedegradation of these sugars (e.g., furfural and hydroxymethylfurfuralfrom degradation of xylose and glucose, respectively) is minimized. Thedifferent parameters of this process—residence time, pH, andtemperature—combine to influence these outcomes. Generally, addition ofless acid will involve conducting this stage at higher temperatureand/or for longer residence time in order to achieve similar resultscompared to a higher acid concentration. Therefore, in accordance withthe present disclosure, the pH of the wet cake and length of the firstpretreatment time and the first pretreatment temperature can be selectedto achieve desired results. In one example, the first pretreatment stagecan be done by selecting a higher pH (i.e., adding less acid) incombination with a higher first pretreatment temperature, a longer firstpretreatment time, or both. In another example, a lower pH is selectedin combination with a lower first pretreatment temperature, a shorterfirst pretreatment time, or both. In still another example, higher pHand lower first pretreatment temperature can be employed with a longerfirst pretreatment time. In another example, a lower pH can be selectedin combination with a lower first pretreatment temperature and a longerfirst pretreatment time.

One aspect of the pretreatment process is that mixing and the selectionof temperature and time can allow for more complete hydrolysis by agiven amount of acid added to the wet cake. Therefore, one potentialresult is a decrease in the amount of acid required to achieve desiredyields of fermentable sugars. In one aspect, this provides for moreefficient use and less waste of acid. The amount of acid can be selectedso as to minimize undesired downstream effects. For example, one mayseek to decrease the amount of sulfur in dried distillers grainsproduced by this method by managing the amount of sulfuric acid used inpretreatment.

The content of solids and liquids in wet cake can influence theeffectiveness of acid in pretreatment. That is, a higher liquid contentmay dilute or buffer the added acid or otherwise reduce the amount ofinteraction between the acid and the lignocellulosic material in the wetcake. In a particular embodiment, preparation of wet cake foracidification can include bringing its solids content to a level of fromabout 15 wt % to about 40 wt %, or more particularly from about 20 wt %to about 35 wt %. In a specific embodiment, acidification can bepreceded by washing the wet cake in a washer 406 to remove a portion ofthe liquid fraction of the wet cake and thereby achieve a desired solidscontent in the wet cake. The washing can also have the benefit ofreducing the buffering capacity of the wet cake, or more particularlythe liquid fraction of the wet cake. Washing can be done with water orother aqueous liquid. In a specific embodiment, liquid reclaimed fromother unit processes or a by-product of such processes, such ascondensate from evaporation of first thin stillage, can be used for thisstep. In an aspect of this embodiment, the liquid fraction removed fromthe wet cake is substantially replaced by a non-buffering, low pH liquid(the condensate).

To facilitate further hydrolysis of cellulose and hemicellulose tofermentable sugars, after the first pretreatment time has concluded asecond pretreatment stage can comprise directing the wet cake to apretreatment reactor 408, wherein the wet cake is subjected to a highertemperature and a higher pressure than those employed in the firstpretreatment stage. In a particular embodiment, the wet cake is heatedto a second pretreatment temperature higher than the first pretreatmenttemperature used in the first stage and held substantially at thattemperature for a second pretreatment time. In a particular embodiment,the second pretreatment temperature is from about 230° F. to about 330°F. According to more specific embodiments, the second pretreatmenttemperature can be from about 245° F. to about 320° F., or from about250° F. to about 300° F., or from about 270° F. to about 300° F., orfrom about 230° F. to about 310° F. In a more particular embodiment, thewet cake is also subjected to a second pretreatment pressure that ishigher than the first pretreatment pressure. Higher pressures at thisstage may be employed to maintain a sufficiently high wet caketemperature.

Heating at this stage can be accomplished by steam injection, or otherheating methods as will be recognized by those of skill in the art withthe aid of the present disclosure. In a particular embodiment, the wetcake is heated before it is transferred to the pretreatment reactor 408,for example by steam injection in transit to the pretreatment reactor408. In another embodiment, the acidified wet cake is heated in thepretreatment reactor 408. As with the first stage, the results of thesecond pretreatment stage can be influenced by the particularcombination of wet cake pH, second pretreatment temperature, and secondpretreatment time. As such, the second pretreatment temperature andsecond pretreatment time can be selected in view of the amount of acidadded during acidification so as to enhance the yield of soluble sugarsand minimize the creation of degradation products.

The high yield of soluble sugars in the first pretreatment stage allowsoperation of the pretreatment reactor 408 at lower temperatures andpressures than might otherwise be required to achieve similar yields ofoligomeric and monomeric sugars. In this way the capital cost and energyexpenditure of pretreatment may be reduced. Lower pretreatmenttemperatures also reduce the amount of undesirable sugar degradationproducts produced, improving the efficiencies of downstream enzymatichydrolysis and fermentation steps. The commencement of hydrolysis in thefirst stage also allows for a relatively short second pretreatment time.In a particular embodiment, the second pretreatment time can be fromabout 3 minutes to about 100 minutes. According to more specificembodiments, the second pretreatment time can be from about 3 minutes toabout 50 minutes, or about 30 minutes to about 80 minutes, or from about5 minutes to about 8 minutes, or from about 20 minutes to about 50minutes. However, it will be understood that a single pretreatmentstage, e.g., the second pretreatment stage, can alternatively be reliedupon to produce sugars from lignocellulosic material in the wet cake inaccordance with the present disclosure.

From the present disclosure and the illustration in FIG. 4, it will beappreciated that a system for pretreating wet cake to produce sugar fromlignocellulosic material contained therein can comprise a mixer 402configured to receive an acid and to receive wet cake, and to mix theacid into the wet cake to produce an acidified wet cake; a pretreatmentvessel 404 operably connected to the mixer 402 and configured to receivethe acidified wet cake from the mixer 402 and agitate the acidified wetcake at a first pretreatment temperature and a first pretreatmentpressure; and a pretreatment reactor 408 operably connected to thepretreatment vessel and configured to receive the acidified wet cakefrom the pretreatment vessel and react the acidified wet cake at asecond pretreatment temperature and a second pretreatment pressure. Thepretreatment reactor 408 can be a reactor designed to operate at thetemperature and pressures discussed above. In a particular embodiment,the reactor is designed so that substantially the entire volume ofacidified wet cake is uniformly exposed to the second pretreatmenttemperature over the second pretreatment time. Possible reactorconfigurations include one or more continuous stirred reactors inseries, one or more batch reactors, or a horizontal or vertical vesselor pipe. In a specific embodiment, the pretreatment reactor 408 is aplug flow reactor. As described above, the pretreatment vessel 404 canbe a cone-bottomed tank equipped with an agitator, or a horizontal pipeor vertical pipe.

In the second pretreatment stage additional polysaccharides in theacidified wet cake are converted to oligomers and monomers, andoligomeric sugars entering this stage are converted to monomers andsmaller oligomers. In an embodiment, the second pretreatment stageprovides a percent yield of soluble glucose of from about 10% to about60%, or an average percent yield of about 35% to about 45%. In a moreparticular embodiment, the yield of monomeric glucose from the secondstage is from about 0% to about 30%, or an average percent yield ofabout 5% to about 10%. In another embodiment, the second pretreatmentstage provides a percent yield of soluble xylose of from about 50% toabout 100%, or an average percent yield of about 90% to about 95%. In amore particular embodiment, the yield of monomeric xylose from thesecond stage is from about 0% to about 65%, or an average percent yieldof about 20% to about 30%. In another embodiment, the secondpretreatment stage provides a percent yield of soluble arabinose of fromabout 40% to about 100%, or an average percent yield of about 85% toabout 95%. In a more particular embodiment, the yield of monomericarabinose from the second pretreatment stage is from about 20% to about100%, or an average percent yield of about 65% to about 75%. In stillanother embodiment, the second pretreatment stage provides a percentyield of soluble galactose of from about 55% to about 100%, or anaverage percent yield of about 85% to about 95%. In a more particularembodiment, the yield of monomeric galactose from the second stage isfrom about 2% to about 100%, or an average percent yield of about 35% toabout 45%. In still another embodiment, the second pretreatment stageprovides a percent yield of soluble mannose of from about 30% to about100%, or an average percent yield of about 75% to about 85%. In a moreparticular embodiment, the yield of monomeric mannose from the secondstage is from about 0% to about 100%, or an average percent yield ofabout 20% to about 30%.

Saccharification can then be performed on the pretreated wet cake,comprising using enzymatic hydrolysis to produce further monomericsugars from oligosaccharides and polysaccharides remaining after thetwo-stage acid pretreatment process. In an embodiment as shown in FIG.5, a method of hydrolyzing lignocellulosic material in wet cake 500 cancomprise: feeding 502 wet cake comprising lignocellulosic material intoa recycling reactor at a feed rate; enzyme addition 504, in which atleast one enzyme is added to the wet cake; and recycling 506 the wetcake and at least one enzyme through the recycling reactor at a recyclerate and for a residence time to hydrolyze the lignocellulosic materialto produce an amount of monomeric sugar in the wet cake.

The embodiment as illustrated further by way of example in FIG. 6.According to the embodiment, the process can comprise feeding theacidified wet cake into a recycling reactor 602 at a feed rate andadding one or more enzymes selected to act upon the oligosaccharides andpolysaccharides. As will be appreciated by those of skill in the artwith the aid of this disclosure, enzymes known to be effective atbreaking up oligosaccharides and lignocellulosic material can be used inthis process, and include various cellulases and hemicellulases, as wellas amylase and beta-glucosidase. More specifically, hemicellulases caninclude xylanase, mannase, galactidase, and arabinase. To facilitateactivity of the enzyme(s), the pH of the wet cake can also be increasedby the addition of a basic solution, either before or after the wet cakeenters the recycling reactor 602. Bases that can be used in this stepinclude, without limitation, ammonia, aqua ammonia, sodium hydroxide,sodium bicarbonate, potassium hydroxide, potassium carbonate, calciumhydroxide, and magnesium hydroxide. Other suitable bases for use in thisstep will be apparent to those of skill in the art having the benefit ofthis disclosure. The wet cake can first be cooled if needed to bring itto a temperature at which the selected enzyme(s) will have the desiredlevel of activity. As illustrated in FIG. 6, cooling can be performed byflashing a vapor off of the wet cake in a flash drum 604. As will beappreciated by those of skill in the art with the aid of thisdisclosure, other approaches and equipment suitable for cooling wet cakecan be employed in addition or in alternative to flashing, includingwithout limitation, multiple flash steps and passing the wet cakethrough one or more heat exchangers.

The process can continue with recycling the wet cake repeatedly throughthe recycling reactor 602 for a selected residence time, during whichthe enzyme(s) is mixed substantially uniformly throughout the volume ofwet cake and begins to hydrolyze the oligosaccharides andlignocellulosic material. In a particular embodiment, the recyclingreactor 602 is operated at a recycle rate that is higher than the massflow rate at which the wet cake is fed into the recycling reactor 602.In an embodiment, the recycle rate is from about 1 to about 10 times thefeed rate. In a more specific embodiment, the recycle rate is from about5 to about 10 times the feed rate. In a still more specific embodiment,the recycle rate is from about 3 to about 6 times the feed rate. Inanother specific embodiment, the recycle rate is from about 1 to about 5times the feed rate.

Outcomes from recycling the wet cake include, but are not limited to,reducing the viscosity of the wet cake entering the recycling reactor602 due to dilution; 2) aiding reduction of the temperature of the wetcake to a target temperature for enzymatic activity; and 3) effectivemixing of the enzyme(s) into the wet cake. In a particular embodiment,the wet cake has a viscosity from 250 cp to 3000 cp upon exiting therecycling reactor 602. In a more specific embodiment, the wet cake has aviscosity of from 500 cp to 2000 cp. In one aspect, the effective mixingallows for using cost-effective amounts of enzymes.

The residence time during which a volume of wet cake and enzyme(s) ispresent in the reactor can be selected to be sufficient to achieve theabove objectives. In a particular embodiment, the residence time is fromabout 6 hours to about 15 hours. In more particular embodiments, theresidence time is from about 10 hours to about 13 hours, or from about12 hours to about 15 hours, or more particularly from about 11 hours toabout 13 hours. In a particular embodiment, the enzymatic hydrolysisprocess is a flow-through process, where the feed rate, recycle rate,and residence time are selected so that each unit volume of wet cakeentering the reactor undergoes substantially similar processingconditions.

From the present disclosure and the illustration in FIG. 6, it will beappreciated that a system 600 for saccharification of lignocellulosicmaterial in wet cake can comprise a recycling reactor 602 configured toreceive wet cake, such as from the flash drum 604, and at least oneenzyme and allow for reaction between the same. The recycling reactor602 can be further configured to receive a recycle stream of the wetcake and enzyme(s) at a recycle rate that is greater than the feed rate.In a particular embodiment, the recycle rate is from about 1 to 10 timesthe feed rate. In a more specific embodiment, the recycle rate is from 1to 3 times the feed rate. In a still more specific embodiment, therecycle rate is from 2 to 4 times the feed rate. The system 600 caninclude a pump operably connected to the recycling reactor 602 thatprovides circulation of the recycle stream at the recycle rate. Therecycling reactor 602 can be further configured to receive a base and tocombine the base and the wet cake.

The residence time may be sufficient for enzymatic hydrolysis to begin,yet it need not be long enough to complete said hydrolysis. Rather,after initial hydrolysis the wet cake and enzymes may be transferred toa fermentation tank 606 where further hydrolysis occurs prior tostarting fermentation. Prior to starting fermentation, the temperatureof the wet cake is reduced from the hydrolysis temperature (typically inthe range of about 120° F. to 150° F.) to the optimum fermentationtemperature (typically about 95° F.). Hydrolysis continues at a slowerrate during fermentation.

In some embodiments, the pretreated wet cake is transferred to one of aplurality of saccharification tanks. The wet cake can first be cooled ifneeded to bring it to a temperature at which the selected enzyme(s) willhave the desired level of activity. The pH in the saccharification tankis adjusted if needed and enzymes are added. In a particular embodiment,the plurality of saccharification tanks are functionally connected inseries to perform saccharification in a serial manner, wherein enzymatichydrolysis is allowed to proceed for a time in the firstsaccharification tank, after which the wet cake is transferred toanother saccharification tank in the series for further enzymatichydrolysis. This transferring step is repeated with the remainingsaccharification tanks in the series, after which the wet cake andenzymes are transferred to the fermentation tank 606. In a specificembodiment, the series can include the recycling reactor 602, into whichthe pretreated wet cake is transferred and in which enzymatic hydrolysisbegins before the wet cake is transferred to the first saccharificationtank. In an aspect, the size and number of saccharification tanks can beadjusted to provide a desired total residence time. In a specificembodiment, the total residence time is from about 35 hours to about 55hours. In a more specific embodiment, the total residence time is about40 hours.

In another particular embodiment, the plurality of saccharificationtanks are configured in parallel to perform saccharification in a batchmanner, wherein a batch of pretreated wet cake is transferred to one ofthe saccharification tanks in which the pH is adjusted if needed,enzymes are added, and enzymatic hydrolysis proceeds for a residencetime, and then the wet cake and enzymes are transferred to thefermentation tank 606. Another batch of pretreated wet cake can betransferred into another one of the saccharification tanks to undergothe same or a similar process. In a more particular embodiment,saccharification comprises using at least three saccharification tankscycling at intervals, for example where one or more saccharificationtanks are holding wet cake undergoing hydrolysis, while one or more ofthe other saccharification tanks are being filled with pretreated wetcake, and one or more of the remaining saccharification tanks aretransferring wet cake and enzymes to the fermentation tank 606. In anaspect, each saccharification tank can be sized so as to hold the wetcake and enzymes for a desired residence time. In a specific embodiment,the residence time is from about 35 hours to about 55 hours. In a morespecific embodiment, the residence time is about 40 hours.

Fermentation creates cellulosic ethanol and carbon dioxide from thesugars in the wet cake. To commence this step, an ethanol-producingmicrobe is added to the wet cake. It will be appreciated by thoseskilled in the art in view of the present disclosure that one or more ofany ethanol-producing microbes, including native and geneticallymodified microbes, may be used, such as Zymomonas mobilis, Saccharomycescerevisiae, Escherichia coli, Bacillus subtilis, and Pichia pastoris. Asindicated above, enzymatic hydrolysis of remaining polysaccharides andoligosaccharides begun in the previous step may continue in thefermentation tank 606. In an aspect of the embodiment, thecontemporaneous fermentation of sugars in the wet cake may promote morecomplete hydrolysis of the polysaccharides by decreasing end-productinhibition of the hydrolysis reactions.

According to one embodiment, hydrolysis and fermentation of wet cakeexiting the recycling reactor 602 may be done in batches among a numberof tanks so that adjacent processes can operate continuously, ifdesired. To accommodate the beer output stream from the fermentationtank 606 and to facilitate controlled delivery to subsequent processes,a batch of beer produced in fermentation tank 606 can be collected in abeer well 608. Carbon dioxide and other vapor streams may be collectedfrom the fermentation tank(s) and the beer well 608 and scrubbed usingtechniques known in the art to remove ethanol and other componentsentrained in the vapor.

Ethanol can be recovered from the beer using any number of techniquesand equipment known in the art to be suitable for this purpose. Moreparticularly, typical techniques, generally termed distillation, involveseparating the liquid and solid components by initiating the transitionof the liquid component to vapor, which is then condensed and collected.Typically, the initial output of this process is a mixture of ethanol,water, and other volatile components. Further steps can be performed onthis mixture to separate ethanol from the other components, typically bymaking use of differences in their respective volatilities. A cellulosicethanol production process is illustrated in FIG. 7, in which the beerproduced by fermentation is transferred from the beer well 608 to adistillation column 702 to produce a cellulosic ethanol stream and alsoa whole stillage by-product, referred to herein as “second wholestillage”, comprising the non-volatile components of the beer. In aparticular embodiment, the second whole stillage is collected into awhole stillage tank 706. In an aspect of the embodiment, the wholestillage tank 706 can be equipped with an agitator.

As will be appreciated by those having skill in the art, the percentageof ethanol and water in the cellulosic ethanol stream after a singledistillation will depend upon many variables, including the type,length, efficiency, and pressure of the column. The cellulosic ethanolstream can be directed to a dehydration system 604 to remove water andother non-ethanol volatile components. In a particular embodiment,dehydration can comprise sending the cellulosic ethanol stream througheither or both of a rectification column, and one or more molecularsieves. In another embodiment, dehydration can comprise sending thecellulosic ethanol stream through a membrane separation system, in whicha pervaporation membrane is used to separate water and ethanol throughdifferential permeation.

The second whole stillage can exhibit particular characteristics thatdistinguish it from the first whole stillage produced by primary ethanolproduction. In one embodiment, as a result of the pretreatment andsaccharification processes of the present disclosure, most or all of thecarbohydrates in the lignocellulosic material in the wet cake feedstockis converted to fermentable sugars, which are then converted to ethanolin fermentation. Therefore, the second whole stillage by-product of thepresent disclosure comprises low weight percentages of residual fiber,starch, and cellulose and a high percentage weight of crude protein. Ina particular embodiment, the second whole stillage has a percent byweight of crude protein from about 40% to about 55%. In more specificembodiments, crude protein content of the second whole stillage is fromabout 40 wt % to about 50 wt %, or from about 35 wt % to about 55 wt %,or from about 35 wt % to about 50 wt %. In another particular embodimentas shown in FIG. 8, protein is filtered from the first whole stillage inthe screener 202 into a filtrate stream as described above and thefiltrate stream is combined with the second whole stillage in the wholestillage tank 706. Agitation can be employed in the whole stillage tank706 to provide thorough mixing of the filtrate into the second wholestillage. One result of the processes described herein is that protein(both plant protein and yeast or other microbes) will constitute asignificant percentage of the total mass of the second whole stillage,making it a good source material for production of high-protein drieddistillers grains and other products derived therefrom.

In accordance with the present disclosure, co-product production fromthe second whole stillage can comprise separating the second wholestillage into its liquid and solid components. Separation techniques andequipment suitable for this process are well-known in the art. In oneembodiment, the second whole stillage can be processed using the same orsimilar approaches as are used in primary ethanol production plants. Inan exemplary embodiment as shown in FIG. 9, the second whole stillagecan be fed from the whole stillage tank 706 into a centrifuge 902, suchas a decanter centrifuge, which separates the second whole stillage intoa semi-solid low-fiber slurry and a thin stillage (termed hereinafter as“second thin stillage”). A dryer 904 can be used to remove residualmoisture from the resulting low-fiber slurry, thereby producing a drieddistillers grains (DDG) having a high protein content.

Dried distillers grains with solubles (DDGS) can be made by recombiningsyrup (produced from the evaporation of first thin stillage) with wetdistillers grains before drying. Accordingly, it is contemplated thatsyrup produced from the evaporation of both first thin stillage andsecond thin stillage can be combined with the low-fiber slurry in makingDDGS in accordance with the present disclosure. However, the inventorshave surprisingly found that a higher quality DDGS may be attainablewhen the low-fiber slurry of the present disclosure is dried without theaddition of the second thin stillage. In this embodiment, syrup producedfrom the first thin stillage from the primary ethanol production plantevaporator 118 is still mixed with the low-fiber slurry prior to drying,but without inclusion of the second thin stillage or syrup producedtherefrom.

In certain embodiments, the DDGS in accordance with the presentdisclosure has a total protein content of from about 40 wt % to about 70wt %. In a more particular embodiment, the DDGS has a total proteincontent of from about 50 wt % to about 65 wt %. In other particularembodiments the total protein content can be from about 45 wt % to about55 wt %, or from about 40 wt % to about 60 wt %, or from about 50 wt %to about 70 wt %. In an aspect of these embodiments, the DDGS also has alow fiber content due to the extent of breakdown and conversion of thefiber in the wet cake feedstock by the two-stage acid pretreatmentprocess and the enzymatic hydrolysis process of the present disclosure.In a more specific aspect, the DDGS comprises fiber in an amount fromabout 0.5 wt % to about 2 wt %. The DDGS in accordance with the presentdisclosure can also include particular nutrients of interest in animalhealth. In one aspect, the DDGS contains glutamic acid in an amount fromabout 6 wt % to about 10 wt %, or more specifically from about 7 wt % toabout 9 wt %. In another aspect, the DDGS contains aspartic acid in anamount from about 1 wt % to about 5 wt % or more specifically from about2 wt % to about 4 wt %. In another aspect, the DDGS contains alanine inan amount from about 2 wt % to about 5 wt % or more specifically fromabout 3 wt % to about 4 wt %. In another aspect, the DDGS containsvitamin A in an amount from about 800 I.U./kg and about 1200 I.U./kg, ormore specifically from about 900 I.U./kg to about 1100 I.U./kg. Inanother aspect, the DDGS contains vitamin E in an amount from about 450I.U./kg and about 650 I.U./kg, or more specifically from about 400I.U./kg to about 600 I.U./kg.

In another aspect, a low fiber content in the DDGS of the presentdisclosure gives it enhanced digestibility and digestible energy. In aparticular aspect, the DDGS has a digestible energy content of at least1500 kcal/lb. In a more specific aspect, digestible energy content isfrom 1500 kcal/lb to about 2000 kcal/lb. In another aspect, low fibercontent imparts particular physical characteristics, such as a fineconsistency and higher density. In a particular embodiment the DDGS hasa density of from about 30 lbs/ft³ to about 40 lbs/ft³, or morespecifically from about 34 lbs/ft³ to about 38 lbs/ft³, or from about 30lbs/ft³ to about 35 lbs/ft³, or from about 34 lbs/ft³ to about 40lbs/ft³.

As noted above, rather than recombination with the low-fiber slurry toproduce DDGS for animal feed, the second thin stillage can be directedto other uses. In co-product production, the second thin stillage can bedirected to an evaporator, where evaporation of water from the secondthin stillage can proceed until the second thin stillage becomes asyrup, or further to produce a substantially solid material, either ofwhich can be used as an animal feed additive. In a particularembodiment, the second thin stillage stream is combined with the firstthin stillage stream for evaporation in the same evaporator, e.g.,evaporator 118. Alternatively, as shown in FIG. 9, the second thinstillage can be directed to an anaerobic digester 906, where anaerobicdigestion can be performed on the second thin stillage to produce abiogas which can be scrubbed and added to existing natural gas pipelinesor the biogas can be used in the primary ethanol plant's boiler. Thisapproach may be undertaken as an effective way to remove the chemicaloxygen demand of the second thin stillage.

Another aspect of the present disclosure with respect to corn-basedethanol production processes is that with less fiber to bind corn oilcontained in the second whole stillage by-product, more of the corn oilis decanted off into the second thin stillage. Accordingly, in oneembodiment a distillers corn oil stream can be obtained from the secondthin stillage. In a particular embodiment, the second thin stillage iscombined with the first thin stillage for further processing, e.g.,evaporation to produce a syrup from which distillers corn oil isextracted. Recovery of corn oil from thin stillage can be achieved byextraction systems and methods known in the art, including evaporation,centrifugation, and solvent extraction. In a specific embodiment, thesecond thin stillage provides an additional yield of DCO of from about0.1 to 0.5 lbs per bushel of corn feedstock. In another specificembodiment, the additional yield of DCO is from about 0.1 lbs to about0.7 lbs per pound of wet cake solids.

It is contemplated that particular benefits may arise from adding one ormore of the processes described above to an existing corn-based ethanolproduction process. In one aspect, this can provide additional ethanolproduction in the form of a cellulosic ethanol stream. As illustrated inFIG. 10 (a portion of which is shown in FIG. 1) which shows an enhancedethanol production plant 1000 in accordance with the present disclosure,a method for increasing ethanol production associated with an existingethanol production plant 100 can comprise feeding wet cake resultingfrom separation of first whole stillage into a cellulosic ethanolproduction process 1002, which can comprise any of the steps andprocesses described above. As illustrated in FIG. 10, equipment for thisadded process can comprise, without limitation, a washer 406 for thestep of washing the wet cake; a mixer 402 for the step of acidificationby mixing acid into the wet cake; a pretreatment vessel 404 for the stepof agitating the acidified wet cake; a pretreatment reactor 408 forperforming the second pretreatment stage; a recycling reactor 602 inwhich the wet cake is recycled with enzymes to initiate enzymatichydrolysis; a fermentation tank 606 for furthering the hydrolysis of thewet cake and fermenting sugars produced in the foregoing processes; anda distillation column 702 to recover a stream of cellulosic ethanol andproduce a by-product of second whole stillage. In a particular exampleas shown in FIG. 10, the cellulosic ethanol stream can be directed to anexisting dehydration system 114 system in the existing ethanolproduction plant 100. In another particular example as shown in FIG. 10,first whole stillage from the distillation system 112 can be filtered ina screener 202 and the resulting filtrate combined with second wholestillage in a whole stillage tank 706, wherein protein contained in thefiltrate bypasses the intervening stages.

In another aspect, a modification of existing corn-based ethanolproduction provides an increased yield of distillers corn oil. Asillustrated in FIG. 10, a method for increasing distillers corn oilproduction associated with an existing ethanol production plant 100 isalso provided by feeding wet cake resulting from centrifuge 116 of firstwhole stillage into a cellulosic ethanol production process 1002. Thesecond whole stillage by-product from the distillation column 702 isseparated with a centrifuge 902 into a low-fiber slurry and second thinstillage. In a particular embodiment as shown in FIG. 10, the secondthin stillage is combined with the first thin stillage for evaporationto produce a syrup from which distillers corn oil is extracted. Thesyrup from the existing ethanol plant's evaporator and the low-fiberslurry can then be directed to a dryer 904 for preparation of a DDGS inaccordance with the present disclosure. The dryer 904 may be dedicatedto drying of the low-fiber slurry and syrup, due to all of the wet cakefrom the existing ethanol production plant being directed to the addedcellulosic ethanol production.

In an alternative embodiment of an enhanced ethanol production plant1100 as shown in FIG. 11, the second thin stillage can be directed to ananaerobic digester 906, where anaerobic digestion can be performed onthe second thin stillage to produce a biogas which can be scrubbed andadded to existing natural gas pipelines or the biogas can be used in theprimary ethanol plant's boiler. This approach may be undertaken as aneffective way to remove the chemical oxygen demand of the second thinstillage.

It will be appreciated from the foregoing that energy expenditures andcosts associated with the added processes can be offset to a degree, notonly by the added value of increased product and co-product streams, butalso by directing process outputs back into appropriate units of theexisting plant. In addition, resources and by-products associated withindividual processes can be re-used or re-purposed. For example, steamgenerated from flashing steps can be used for heating in other stepssuch as acidification and pretreatment, as well as for driving beerthrough distillation columns. In addition, the enhanced productionprovided by the processes described herein allow existing ethanolproduction plants to forego resource-intensive corn milling techniques(e.g., wet milling) in preparing the corn feedstock for use.

EXAMPLE EMBODIMENTS Example 1

Corn wet cake from primary ethanol production was subjected to thefollowing cellulosic ethanol production process to produce a drieddistillers grains with solubles. Steps 1-5 were performed at an ethanolplant modified according to embodiments herein. Steps 6-9 were performedat a research center according to embodiments herein.

-   -   1. The corn wet cake (3,473 lbs, 32% solids) was mixed in an        agitated cone bottom tank with 135 gallons of process condensate        (water) and 85 lbs of 40 wt % sulfuric acid;    -   2. The acidified wet cake was heated with direct steam injection        to about 190° F. and held at that temperature for one hour        (i.e., first pretreatment);    -   3. The wet cake was pumped through a horizontal plug flow        reactor at about 280° F. with a residence time of 25 minutes        (i.e., second pretreatment);    -   4. Wet cake was continuously discharged from the reactor to the        flash tank and then to the enzymatic hydrolysis tank. The        temperature of the wet cake was lowered to 140° F. and the pH        was adjusted to 4.5 with aqueous ammonia, and cellulase and        hemicellulase enzymes were added;    -   5. Hydrolysis proceeded for about 50 hours; the temperature was        lowered to 95° F. followed by addition of a GMO saccharomyces        yeast and fermentation for about 50 hours;    -   6. The resulting beer was distilled in a beer column;    -   7. The whole stillage was decanted in a centrifuge to produce a        second wet cake and thin stillage (i.e., second thin stillage);    -   8. The thin stillage was evaporated to produce syrup;    -   9. The syrup was combined with the second wet cake and dried in        a ring dryer to produce DDGS having the following properties:

TABLE 1 Chemical and Physical properties of typical dried distillersgrains with solubles (DDGS) produced from the cellulosic ethanol processdescribed above. The DDGS exhibited a typical density of 35-37 lbs/ft³.Chemical and Physical Properties Min Max Moisture % — 13.0 TotalProtein, % 40.0 — Fiber (crude), % — 2.0 Fat (crude), % 1 — Ash, % 8.0

TABLE 2 Energy analysis of the dried distillers grains with solubles.Energy Typical, d.b. Kcal/lb kcal/kg Digestible Energy 1600 3530Metabolizable Energy 1100 2425 Net Energy Gain 600 1320 Net EnergyMaintenance 900 1985 Net Energy Lactation 800 1765 Total DigestibleNutrients, % 88

TABLE 3 Nutritional content of the dried distillers grains withsolubles. Nutrients Typical, % DM Protein 45 Fat 1.5 Fiber 1.5 ADF 3.5NDF 4 Ash 8 Alanine 3.6 Arginine 1.5 Aspartic Aid 2.8 Cystine 0.8Glutamic Acid 8.9 Glycine 1.7 Histidine 1 Isoleucine 1.7 Leucine 5.6Lysine 1 Methionine 1 Phenylalanine 2.3 Proline 3.9 Serine 2.4 Threonine1.7 Tryptophan 0.3 Tyrosine 1.7 Valine 2.2 Vitamins Vitamin A, IU/100 g107.2 Vitamin E IU/kg 535 Niacin mg/kg 19.6 Inositol mg/100 G 2020 FolicAcid mg/kg 0.89 Protein-Ruminants Estimated RUP, % CP 69 Rumen, % CP 41Intestine, % CP 42 Total digested, % CP 74 Minerals Typical, as isMagnesium, % 0.5 Phosphorus, % 1.7 Potassium, % 1.7 Chloride, % 0.2Sulfur, % 1.7 Calcium, ppm 300 Sodium, ppm 400 Copper, ppm 8.6 Iron, ppm795 Manganese, ppm 25 Selenium, ppm 0.2 Zinc, ppm 79

Example 2

The effect of three parameters (% acid added, temperature, and residencetime) were measured in forty-three trials in which corn wet cake wassubjected to a two-stage pretreatment process similar to Steps 1-2(first pretreatment stage) and Step 3 (second pretreatment stage) inExample 1. The yields of soluble sugars and monomeric sugars resultingfrom each stage are shown below.

TABLE 4 Percent yields of five soluble sugars produced in the firstpretreatment stage. First Pretreatment % Acid Temp Time Yield of TotalSoluble Sugars Stage Added (° F.) (min) Glucose Xylose GalactoseArabinose Mannose Average 3.7 188 64 39.0%  96.8%  94.7%  98.4%  83.4%MIN 2.0 162 10 19.3%  87.3%  64.6%  91.2%   0.0% MAX 6.2 196 307 51.3%100.0% 100.0% 100.0% 100.0% Std Dev 0.9 8.6 67  6.2%   3.5%   8.2%  2.4%  22.6%

TABLE 5 Percent yields of five monomeric sugars produced in the firstpretreatment stage. First Pretreatment % Acid Temp Time Yield ofMonomeric Sugars Stage Added (° F.) (min) Glucose Xylose GalactoseArabinose Mannose Average 3.7 188 64 1.7%  7.1% 11.6% 52.0% 16.1% MIN2.0 162 10 0.0%  0.7%  3.0%  2.3%  0.0% MAX 6.2 196 307 7.9% 20.4% 42.1%89.8% 69.4% Std Dev 0.9 8.6 67 2.3%  4.4%  7.9% 16.1% 17.1%

TABLE 6 Percent yields of five soluble sugars produced in the secondpretreatment stage. Second Pretreatment % Acid Temp Time Yield of TotalSoluble Sugars Stage Added (° F.) (min) Glucose Xylose GalactoseArabinose Mannose Average 3.8 268 32 41.2%  92.8%  91.6%  90.9%  81.0%MIN 2.0 244 3 16.4%  54.0%  63.5%  46.2%   0.0% MAX 6.2 320 205 52.4%100.0% 100.0% 100.0% 100.0% Std Dev 1.0 15 28  6.1%   7.7%  10.1%   8.8% 21.1%

TABLE 7 Percent yields of five monomeric sugars produced in the secondpretreatment stage. Second Pretreatment % Acid Temp Time Yield ofMonomeric Sugars Stage Added (° F.) (min) Glucose Xylose GalactoseArabinose Mannose Average 3.8 268 32  7.6% 25.3% 40.6% 70.4%  23.4% MIN2.0 244 3  0.0%  2.8%  5.6% 22.1%   0.0% MAX 6.2 320 205 20.4% 60.0%99.3% 96.4% 119.8% Std Dev 1.0 15 28  5.5% 13.8% 20.3% 10.8%  26.8%

The above yields were determined by liquid chromatography. It isbelieved that the results reported for mannose, particularly the minimumpercent yields (“MIN”), may reflect interference from other compounds inthe samples.

While specific embodiments and applications have been illustrated anddescribed, it is to be understood that the invention is not limited tothe precise configuration and components disclosed herein. Variousmodifications, changes, and variations which will be apparent to thoseskilled in the art may be made in the arrangement, operation, anddetails of the methods and systems of the present invention disclosedherein without departing from the spirit and scope of the invention.

What is claimed is:
 1. A method for producing a sugar fromlignocellulosic material in fermentation residual material, comprising:a. mixing an amount of an acid into the fermentation residual material;b. agitating the fermentation residual material and the acid for a firstpretreatment time at a first pretreatment temperature for a firstpretreatment stage; and c. pretreating the fermentation residualmaterial with the acid in a pretreatment reactor for a secondpretreatment time at a second pretreatment temperature for a secondpretreatment stage, wherein the second pretreatment temperature ishigher than the first pretreatment temperature and the secondpretreatment pressure is higher than the first pretreatment pressure,and wherein the lignocellulosic material is converted to a soluble sugarat a percent yield from about 5% to about 100% upon completion of thefirst pretreatment stage.
 2. The method of claim 1, wherein the solublesugar includes at least one of the group consisting of glucose, xylose,mannose, arabinose, and galactose.
 3. The method of claim 1, wherein thefirst pretreatment temperature is from about 170° F. to about 225° F. 4.The method of claim 1, wherein the acid is a mineral acid.
 5. The methodof claim 4, wherein the mineral acid is selected from the groupconsisting of sulfuric acid, phosphoric acid, hydrochloric acid,hydrofluoric acid, formic acid, nitric acid, and mixtures thereof. 6.The method of claim 1, wherein the acid is an organic acid.
 7. Themethod of claim 6, wherein the organic acid is selected from the groupconsisting of maleic acid, oxalic acid, acetic acid, fumaric acid, andmixtures thereof.
 8. The method of claim 1, wherein the amount of acidis such that the fermentation residual material has a pH of from about1.5 to about 2.5.
 9. The method of claim 1, wherein the firstpretreatment pressure is at atmospheric pressure and the firstpretreatment temperature is from about 170° F. to about the boilingpoint of water.
 10. The method of claim 1, wherein the pretreatmentreactor is selected from the group consisting of a plug flow reactor, acontinuous stirred reactor and a pressurized pipe.
 11. The method ofclaim 1, wherein the first pretreatment time is from about 15 minutes toabout 300 minutes.
 12. The method of claim 1, further comprising thestep of washing the fermentation residual material to reduce a bufferingcapacity of the fermentation residual material before the mixing step.13. A method for hydrolyzing lignocellulosic material in fermentationresidual material, comprising: a. feeding a fermentation residualmaterial comprising lignocellulosic material into a recycling reactor ata feed rate; b. adding at least one enzyme to the fermentation residualmaterial; and c. recycling the fermentation residual material and atleast one enzyme through the recycling reactor at a recycle rate and aresidence time to hydrolyze the lignocellulosic material to produce anamount of monomeric sugar in the fermentation residual material.
 14. Themethod of claim 0, further comprising directing the fermentationresidual material and at least one enzyme to a fermenter and fermentingthe monomeric sugar using a microbe.
 15. The method of claim 0, whereinthe recycle rate is from about 1 to about 10 times the feed rate. 16.The method of claim 0, wherein the residence time is from about 6 hoursto about 15 hours.
 17. The method of claim 0, wherein the at least oneenzyme is selected from the group consisting of cellulase, xylanase,arabinase, galactidase, mannase, amylase, and beta-glucosidase.
 18. Amethod for increasing ethanol production from lignocellulosic biomass,comprising, a. providing an ethanol production plant comprising aplurality of processes for producing a first ethanol stream with abyproduct of a fermentation residual material containing lignocellulosicmaterial; and b. adding to the ethanol production plant a cellulosicethanol production process comprising: i. pretreating the fermentationresidual material with an acid in two stages to hydrolyze a fraction ofthe lignocellulosic material into soluble sugars; ii. saccharifying thefermentation residual material with an enzyme to hydrolyze a fraction ofthe soluble sugars into fermentable sugars; iii. fermenting thefermentable sugars in the fermentation residual material to producecellulosic ethanol; iv. distilling the cellulosic ethanol from thefermentation residual material to produce a cellulosic ethanol streamand a second whole stillage, wherein the second whole stillage has acrude protein content of from about 40 wt % to about 55 wt %; and v.removing water from the first ethanol stream and the cellulosic ethanolstream.
 19. A method for ethanol production with increased corn oilyield, comprising, a. providing an ethanol production plant comprising:distilling a first ethanol stream from fermented corn to yield a firstwhole stillage, and separating the first whole stillage into a firstthin stillage and a corn wet cake comprising lignocellulosic material;and b. adding to the ethanol production plant a cellulosic ethanolproduction process comprising: i. pretreating the corn wet cake with anacid in two stages to hydrolyze a first fraction of the lignocellulosicmaterial into soluble sugars; ii. saccharifying the corn wet cake withan enzyme to hydrolyze a fraction of the soluble sugars and a secondfraction of the lignocellulosic material into fermentable sugar; iii.fermenting the fermentable sugar in the corn wet cake to producecellulosic ethanol; iv. distilling the cellulosic ethanol from the cornwet cake to produce a cellulosic ethanol stream and a second wholestillage; v. separating the second whole stillage into a second thinstillage and a low-fiber slurry; and vi. evaporating the first thinstillage and the second thin stillage to produce a syrup stream and thenseparating distillers corn oil from the syrup stream, wherein the amountof lignocellulosic material converted in the pretreating andsaccharifying steps results in an increase of about 0.1 lb/bushel to 0.5lb/bushel increase in distillers corn oil recovered.
 20. The method ofclaim 0, further comprising the step of washing the corn wet cake toreduce a buffering capacity of the corn wet cake before the pretreatingstep.